I. Technical Field
This invention pertains to telecommunications, and particularly an inter-radio access technology (IRAT) and inter-frequency measurement(s) involved with neighbor relation list management.
II. Related Art and Other Considerations
In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units (UE) such as mobile telephones (“cellular” telephones) and laptops with wireless capability), e.g., mobile termination), and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or “B node”. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions (particularly earlier versions) of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
Specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within the 3rd Generation Partnership Project (3GPP). The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).
An inter-radio access technology (RAT) handover is process wherein a mobile terminal switches from using a first radio access system having a first radio access technology (such as GSM) to a second radio access system having a second radio access technology (such as UTRA). Inter-RAT handover is normally initiated when the quality of a downlink radio connection of the first radio access network falls below a certain level. Inter-radio access technology (RAT) handovers are described, e.g., in U.S. Pat. No. 7,181,218, entitled “COMMANDING HANDOVER BETWEEN DIFFERING RADIO ACCESS TECHNOLOGIES”, which is incorporated herein by reference in its entirety.
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are performed by the radio base stations nodes. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
The evolved UTRAN (E-UTRAN) comprises evolved base station nodes, e.g., evolved NodeBs or eNBs, providing evolved UTRA user-plane and control-plane protocol terminations toward the user equipment unit (UE). The eNB hosts the following functions (among other functions not listed): (1) functions for radio resource management (e.g., radio bearer control, radio admission control), connection mobility control, dynamic resource allocation (scheduling); (2) mobility management entity (MME) including, e.g., distribution of paging message to the eNBs; and (3) User Plane Entity (UPE), including IP Header Compression and encryption of user data streams; termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. The eNB hosts the PHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. The eNodeB also offers Radio Resource Control (RRC) functionality corresponding to the control plane. The eNodeB performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of DL/UL user plane packet headers.
2G and 3G systems, including E-UTRAN, make use of Mobile Assisted handover (MAHO). Each mobile station (MS) periodically monitors the signal quality of the serving base station (BS) as well as the signal quality of base stations in its surroundings and may report the measurements back to the serving radio base station. The radio network typically initiates handovers based on these measurements. As an example, consider the case of a prepared handover (HO) in E-UTRAN. The target or candidate base station (BS), which the mobile station (MS) will be handed off to, gives guidance for the mobile station (MS) on how to make the radio access, e.g., radio resource configuration and necessary identities. Further, the serving base station (BS) needs to forward user plane data to the target base station (BS), meaning that the target base station (BS) must be known and its unique identity, so-called Cell Global Identity (CGI), must be established before executing the HO.
Typically, there is also a local identifier (ID) defined for each base station (BS). The local ID of a base station (BS) is used for layer-1 measurements and is not long enough to be unique within the network. For example, a mobile station (MS) reports the signal quality of a base station (BS) along with its local ID to the serving base station (BS). The local ID is not enough for a handover (HO), since the local ID is not unique within the network. As such, when handing off a mobile station (MS) to the neighbor the CGI of the neighbor must be known. The neighbor relation list (NRL), thus constitutes or is at least involved in the mapping from the local ID to the Cell Global Identity (CGI) and possibly also other information such as the IP address of the target base station (BS).
It is envisioned that E-UTRAN will initially have a limited radio coverage. To provide seamless mobility it is necessary to Hand Over (HO) mobile stations (MSs) in E-UTRAN to an alternative Radio Access Technology (RAT) such as GSM EDGE Radio Access Network (GERAN) or UTRAN with better coverage. It is also desired for a mobile station (MS) served by 2G (e.g. GERAN) or 3G (e.g. UTRAN), to switch to E-UTRAN once the mobile station (MS) is within the coverage of E-UTRAN. The latter is desired since higher data rates are offered by E-UTRAN, enabling services with greater bandwidth requirements. Handover between two different RATs is referred to as an inter-RAT (IRAT) handover. Further, it is projected that LTE will operate in multiple frequency bands. To handle issues like load balancing between different frequency bands, which require inter-frequency handovers (HO), IRAT and inter-frequency neighbor relation lists (NRLs) are established.
One focus area in E-UTRAN standardization work is to ensure that the new network is simple to deploy and cost efficient to operate. The vision is that the new system shall be self-optimizing and self-configuring in as many aspects as possible. See, e.g., 3GPP TR 32.816, Study on Management of E-UTRAN and SAE.
For inter-RAT/frequency HOs the serving base station (BS) needs to be able to trigger inter-RAT/frequency measurements, make a comparison between different RATs/frequencies, and make a HO decision. The following events typically need to be performed to prepare for HOs from a serving base station (BS) to a target base station (BS) (e.g. from a E-UTRAN BS to a UTRAN BS) as shown in FIG. 13 (the axes represent serving and candidate BS quality):                If the estimated signal quality of the serving base station (BS) falls below a certain threshold (threshold A in FIG. 13), then inter-RAT/frequency measurements performed by the mobile station (MS) are triggered.        If the estimated signal quality of the serving base station (BS) rises above a certain threshold (threshold A in FIG. 13), then inter-RAT/frequency measurements performed by the mobile station (MS) are stopped.        If the estimated signal quality of the serving base station (BS) is below a certain threshold (threshold A in FIG. 13) and the estimated signal quality of the candidate base station (BS) is above a threshold (B in FIG. 13), then the inter-RAT/frequency HO procedure may be initiated.        
For a mobile station (MS) with a single receiver, the receiving frequency of the mobile station (MS) has to be altered when carrying out inter-RAT/frequency measurements. When changing the frequency (during inter-RAT/frequency measurements), the mobile station (MS) is not able to communicate with the serving RAT. The state during which the mobile station (MS) carries out inter-RAT/frequency measurements is called the reading gap. The serving base station may avoid transmissions to the mobile station (MS) during the reading gap. The state during which a base station does not transmit to a mobile station (MS) is referred to as a transmission gap. Note that, in order for the mobile station (MS) to use the time of the transmission gap for inter-RAT/frequency measurements, a reading gap must be issued. From now on, it is assumed that a reading gap is always issued by the concerned mobile station (MS) when the serving base station (BS) issues a transmission gap. A reading gap can however be issued by the mobile station (MS) even if no transmission gap has been issued by the base station (BS). The gaps may occur periodically according to a predefined pattern, as shown in FIG. 14, or may be event-triggered. Further, the length of the gaps may be fixed or varying.
Some RATs, e.g., E-UTRAN and UTRAN, support dynamic scheduling of uplink (UL) and/or downlink (DL) data, where radio resources are assigned to users and radio bearers according to the users momentary traffic demand, QoS requirements, and estimated channel quality. The base station (BS) may assign radio resources in time or frequency to mobile stations with, e.g., higher channel quality. The smallest schedulable resource entity is hereafter called a Scheduling Block (SB).
As an example, in E-UTRAN, the scheduling block (SB) comprises two consecutive resource blocks, with a total length of 1 ms and width of 180 kHz, see FIG. 15. In this case, the base station (BS) allocates SBs to mobile stations both in time and frequency. In E-UTRAN, a mobile station (MS) may be configured to report Channel Quality Indicator (CQI) reports, indicating the quality of the DL. Based on the CQI reports and QoS requirements the scheduler assigns SBs.
Previously in 2G (e.g., GERAN) and 3G (e.g., UTRAN) systems NRL lists have been populated using planning tools by means of coverage predictions before the installation of a base station (BS). Prediction errors, due to inaccuracies in topography data and wave propagation models, have forced the operators to resort to drive/walk tests to completely exhaust the coverage region and identify all handover regions and as such the neighbors. Since a radio network gradually evolves over time with new cells and changing interference circumstances, traditional planning of NRL requires iterative repetitions of the planning procedure. This has proven to be costly and new methods for automatically deriving NRLs are required. Thus, it is essential to make use of automatic in-service approaches for generating and updating NRLs.
The known existing solution aiming at automating NRL management only address one particular RAT, e.g., GERAN or UTRAN. See, e.g., PCT Patent Application PCT/EP2007/001737, filed Feb. 28, 2007, which is incorporated herein by reference in its entirety. Even though NRL management has been automated for one type of RAT, the problem of establishing NRLs for different RATs/frequencies has not been solved before. Traditionally, these inter-RAT/frequency NRLs have been manually derived using topographical information and drive/walk testing. This has proven to be rather tedious and costly and new automated methods where the network itself establishes and configures the NRLs are needed.
What is needed therefore, and an object of this invention, are apparatus, methods, and techniques for establishing and managing inter-RAT measurements and information, such as that utilized by a neighbor relation list for inter-RAT/frequency mobility.